Understand color of Diffuse Direct/Indirect pass in Cycles render
I'll try to explain. Here is an example.
We have an orange ball on the gray plane, lit from the side.



What contains the Diffuse Direct pass? A reflection of light coming from the lamp on the side. As you can see, the layer does not contain information about that the ball is orange.



To get the orange color you need to multiply Diffuse Direct and Diffuse Color.

What contains the Diffuse Indirect pass? light reflected from the ball becomes orange and this light illuminates the plane. And the plane reflects light almost unchanged, so the ball looks white:



Finally, connect all layers together 

 

You can see, gray plane have orange reflect from sphere. This reflection goes from indirect pass. 

So if Diffuse Direct and Diffuse Indirect are just gray-scale images, where were no color reflexes in scene